The scene outside the American embassy on a hot summer day in 1996 would have been a familiar one in a hundred different cities: a long line of aspiring emigrants waiting patiently at the visa window for a form to fill in or an appointment to make.

But the nervous Sudanese man in the queue had something else in mind. "I don't want visa," he said in broken English. "But I have some information for your government... about people, they want to do something against your government."

That was over four years ago. We still do not know the location of the embassy - it remains secret for reasons of US national security - but we do know the name of the Sudanese man in the queue. It is Jamal Ahmed al-Fadl, and the people he wanted to warn the US embassy about were his former employers, Osama bin Laden and his al-Qaeda organisation.

Mr al-Fadl, now 37 years old, has a new identity under a federal witness protection programme, along with $20,000 (£13,500) as starting capital for a new life. Since his defection, he has been referred to in official documents as CS1 (Confidential Source One).

But he has resurfaced under his real name this month in New York as a star witness in the trial of four men accused of plotting, on Mr Bin Laden's orders, the 1998 bombing of the US embassies in Kenya and Tanzania in which 224 people were killed.

As he defected two years before the bombs went off, Mr al-Fadl can say nothing about the events of that bloody August in east Africa, but what he did provide in the Manhattan courtroom has been riveting none the less. As a founding member and trusted official in al-Qaeda (roughly translated as the Base), he was in a perfect position to give a comprehensive account of its far-reaching operations.

He gave evidence in faded jeans and a white knitted skull cap. The court artist was not permitted to draw his portrait.

Modern

Like any other multinational enterprise in the era of globalisation, al-Qaeda appears to have diversified its product, producing roads and bridges as well as bombs and booby traps. It is arranged, not in an old-fashioned vertical hierarchy, but in a modern horizontally integrated array of loosely affiliated groups, drawing shared goals and philosophy from the centre but operating independently. It is as if Mr Bin Laden had been consulting the most up-to-date management gurus.

What Mr al-Fadl had to say helped explain why his former boss appears so powerful and invincible and, paradoxically, why his sudden death or disappearance would be unlikely to stem the unpredictable violence in which al-Qaeda specialises.

The most striking feature of Mr al-Fadl's testimony was all the banal detail of the nine-to-five grind of a career in terrorism.

In al-Qaeda's offices in Khartoum, the boss sat in the first office on the left. There were board meetings, wage nego tiations and the firm took care of its employees' healthcare. There were perks for employees, such as free tea and groceries, and an in-house specialist for the interpretation of dreams. A travel department obtained tickets and passports to order.

As in all multinational corporations, al-Qaeda appears to suffer from constant friction and mutual envy among the various national groups working for it.

Mr al-Fadl had joined the organisation at the beginning, in Afghanistan in 1990, when Mr Bin Laden, the maverick heir to a Saudi construction fortune, decided to divert the money and resources he had poured into the mojahedin war against the Soviet Union in Afghanistan, and channel into a new jihad - against the "snake", the United States.

Mr al-Fadl recalled Mr Bin Laden and his closest advisers issuing a fatwah against the US at the time of the Gulf war. He said: "The fatwah, it say we cannot let the American army stay in the Gulf area and take our oil, take our money and we have to to do something to take them out. We have to fight them."

When the newly formed al-Qaeda decamped to Sudan on the invitation of a radical Islamic regime in Khartoum, Mr al-Fadl became a trusted employee. He once delivered $100,000 in cash to an al-Qaeda member in Jordan (where the organisation arranged for customs officers to overlook the dollar-stuffed bag), and on another occasion he was sent off with enough money to buy 50 camels to smuggle weapons into Egypt.

But he bristled at the fact that the Egyptians in the organisation earned far more than his $500 a month and appeared to wield more clout. He confronted his boss with his complaints, but Mr Bin Laden told him the Egyptians were paid extra to help them visit their families back home.

"He say ... some people, they got citizenship from another country and they go back over there for regular life," Mr al-Fadl told the court. "And he says that's why he try to make them happy and give them more money."

Mr al-Fadl was not appeased and decided to top up his salary himself, skimming off a total of $110,000 in the form of under-the-counter commissions for contracts awarded. He was caught, but Mr Bin Laden ordered him to repay the money in order to gain forgiveness.

However, the world's most feared terrorist may have been too laid back for his own good. Mr al-Fadl could not repay the money and instead fled Sudan and ran into the arms of the CIA. He must have been a heaven-sent source for the agency with a detailed inside picture of Mr Bin Laden's organisation.

By the time it reached the southern district court in Manhattan it was of course, already out of date. Mr Bin Laden has since decamped to Afghanistan, and the Sudanese operation has been rolled up. But Mr al-Fadl's testimony still says a lot about his organisational style.

In Sudan, according to Mr al-Fadl, al-Qaeda had a board of directors, the Shura council, a panel of a dozen or so trusted lieutenants, which discussed and coordinated all the organisation's far-flung activities.

Subordinate to the council were four executive committees: military, responsible for weapons and training; money and business, in charge of all al-Qaeda's commercial operations as well as personnel, salaries and healthcare; Islamic study, charged with maintaining the theological rigour of the organisation; and media, which ran a weekly newspaper. Its editor wrote under the ironic pen name of Abu Massad Reuter, in honour of the British news agency, Reuters.

The organisation ran a network of money-making ventures in Sudan under an umbrella holding corporation called Wadi al-Aqiq, which Mr al-Fadl referred to as "the mother of all companies". Its subsidiaries included Ladin International, an import-export company; Taba investment; which traded currencies; Hijra Construction, a civil engineering company and Themar al-Mubaraka, which ran a farm growing sesame seeds, peanuts and corn.

All these disparate enterprises were aimed at propagating al-Qaeda's core "product", jihad (or holy war). The commercial groups helped sustain Mr Bin Laden's fortune, which either financed al-Qaeda terrorist operations or sponsored a wide variety of like-minded groups from around the world, who came for weapons training and bomb-making instruction at the Themar al-Mubaraka farm in Sudan.

Many of the trainees were Egyptians from the Islamic Jihad movement. Its leader, Ayman al-Zawahiri has emerged as Mr Bin Laden's deputy. Other al-Qaeda clients have included Filipino Muslim separatists, Algerians (like the Montreal cell broken up last year after Ahmed Ressam tried to smuggle explosives over the US border near Seattle) and Yemenis (like the group that carried out the boat-bomb attack on the USS Cole).

'Franchise'

There were also Arab Americans like two of the defendants in the New York trial: Wahid el-Hage, the manager of a shop in Dallas and Ali Mohamed, an Egyptian-born former US army sergeant who was assigned to instruct special forces on Islamic politics and culture. It turns out that he remained an agent for Egyptian Islamic Jihad.

All these cells operated on their own, but they looked for money, training and direction to the centre and al-Qaeda.

"In corporate terms, it's not IBM but more like a franchise, like Kentucky Fried Chicken," Brian Jenkins, a US terrorism expert, said. "One of the trends we have seen in terrorism organisations in the last 10 years is that they have become a lot more fluid. There are a lot more networks than the more traditional hierarchies. Al-Qaeda has done away with layers of middle management, but its still able to maintain its 'brand'."

This "branding", Mr Jenkins suggests, represents the "return" Mr Bin Laden accrues on his investments in disparate acts of terrorism. Increasingly the west attributes them to him, solidifying his legendary status in the angry refugee camps and impoverished slums of the Arab world.

The myth was burnished further last week when the CIA director, George Tenet, called Mr Bin Laden the "most immediate threat to America's national security".

By pressuring Sudan to expel Mr Bin Laden, the US has managed to raise his operating costs. Patrick Clawson, the research director at the Washington Institute for Near East Policy said: "He is no longer in the heart of the Arab world. It is very different trying to operate out of Afghanistan where every movement in and out is going to be suspicious."

The point was underlined yesterday when it was announced that two Saudi men, a father and son, had been arrested by Pakistani police on the Afghan border carrying cash to Mr Bin Laden. However, it is thought that al-Qaeda is still able to move most of its funds around with the aid of the internet and state-of-the-art encryption devices.

Just as modern, flexible business organisations can rapidly adapt to changing markets, so can al-Qaeda. The portrait being painted in court this month is a rapidly-fading snapshot of the past.

The organisation has shown its ability to mutate a hundred times since then. To keep up, western counter-intelligence must rely on all the satellite surveillance tools at its disposal, together with the hope that one day, another underpaid al-Qaeda clerk will show up at the visa window of another US embassy.